A large number of optical devices rely on amorphous material such as glass or on crystalline materials or on structures comprised of intervening layers of crystalline or amorphous materials for providing desired optical characteristics. Some optical devices utilize a coherent Bragg scattering characteristic of a periodic layered structure to achieve a desired optical property. For example, devices such as semiconductor distributed feedback (DFB) lasers and Bragg optical filters rely on such properties.
A particular problem associated with such optical devices is the required construction of a layered optical device having very small inter-layer dimensions, the dimensions being on the order of half that of the wavelength of the radiation of interest. For example, it has been known to utilize molecular beam epitaxy (MBE) and organometalic chemical vapor deposition (OCVD) techniques to form DFB semiconductor lasers which are comprised of a plurality of thin layers of semiconductor material. As can be appreciated, in any such device the fabrication process is an important and costly consideration. For example, any variations in layer thicknesses or in surface roughness between the layers may cause undesirable optical effects to occur. Additionally, another problem associated with such devices is that the lower limits of currently available semiconductor layer formation techniques, and also photolithography, may not be suitable for providing a device having the desired thickness and spacing of Bragg reflective layers. Thus, a lower limit is approached on the wavelengths of radiation which may be employed with these devices.
Another problem associated with prior optical devices relates specifically to nonlinear optical devices such as birefringent and polarization sensitive devices. The hyperpolarizability of conventional devices may not be optimum for some applications. Furthermore, these conventional devices may be fragile, costly and have a response limited to a narrow range of wavelengths.
One further problem associated with prior optical devices relates to those types of devices which comprise a dipolar dye having a desired radiation absorption and emission characteristic. In some conventional devices it may be necessary to provide an external electrical field to orient the dye molecules in a desired configuration. It has been known to utilize a crystalline colloidal structure having a plurality of parallel, spaced apart planes as a passive Bragg diffracting filtering device for separating a narrow wavelength band from a broader spectrum of electromagnetic radiation, as is shown in U.S. Pat. Nos. 4,627,689 and 4,632,517 to S. A. Asher.